David - unwrapped jpgs already support this. The xmp spec allows for all non-destructive parametric edits to be written as xmp metadata to jpg files. In fact, this info is written to jpgs in almost exactly the same format as it is in a dng.

- Non-destructive editing - unwrapped jpgs already support this via xmp metadata.
- Hash validation - OK: I assume jpgs do not support this, or an equivalent, although I don't know. This sounds worthwhile.
- Embedded preview: Check - non-destructive jpg edits are only visible in Lightroom or bridge. The dng preview would allow visibility in any app supporting dng. - Good one..
- No likelihood of another program writing changes to the file - gotcha. This would be a plus.

Now I'm in a dilemma: I dont use DNG, but if I did I would want this FR/Idea. Do I vote for it formally? - Or just say informally:

Let me clarify the nondestructive editing point. If I email a jpg to someone, it would never occur to them to open it in LR to see what edits have been made. In fact, I always export out of LR before emailing anything so I'm not even sure whether Windows/Mac will show them the edited or original version... In any event, if you send them a dng, they immediately know to open in ACR or LR and can see your edits, which can be helpful when working collaberatively.

Point taken / distinction noted... - in fact, even if they did not know to open in ACR/LR, any DNG reader would recognize the preview, whereas if someone opened the jpg in a generic viewer, it would just look like you hadn't edited it... - I think you "win" this one... - I gave you the vote ;-}

Yes, this is now implemented in Lr 4 / ACR 7 with DNG 1.4 support. The JPEG can now be effectively contained within a DNG, without increasing the file size significantly, and without loss of quality (doesn't require decompressing/recompressing the image data).

One could almost argue that it makes sense now to wrap all jpeg masters in a DNG, that way there is never the mistake of thinking a jpeg is baked, when it's not, as well as the other benefits cited above.

On the other hand, there is presently no way to distinguish a pure-raw DNG, from a lossy-compressed-raw DNG, from a reduced-rez DNG, from a jpeg-wrapped-in-a DNG, or is there? One could argue that it doesn't matter, but people like me, like to know... ;-}

(Obviously filesize is a clue, but that only gets you so far...)

Now how about that option to auto-convert PNGs to DNG upon import?

PS - If Adobe created an un-DNG feature, I'd convert all my photo files to DNG today. But as it stands, it's a one-way feature, which means a "lifetime" commitment to Adobe software for processing (or a roll-yer-own un-DNG'r, if you have enough technical prowess, or maybe Adobe or somebody else will write one at some point...).

Yes, there is a way to know. Use the metadata panel in Lr 4 and select "DNG" from the popup. That will tell you the pixel data type, whether it's lossy compressed, the DNG version, whether it's a mosaic image or not, etc.

You can also use the File Type filter in the Filter headers in Library to pick out certain DNG file types (e.g., lossless compressed ones).

And I disagree with your comment about converting to DNG implying you are bound to use the Adobe software. There are several other raw converters out there that read and process DNG. Perhaps you may not prefer to use those converters, but to suggest that one is limited to using Adobe software to process DNGs is incorrect.